The present invention relates generally to monitors, and more particularly relates to level monitors for determining the levels of materials in such things as bins.
Rotary paddle bin monitors are used to monitor the level of dry bulk materials at various single points in storage bins, hoppers, tanks, silos or other structures. Monitor units can be installed almost anywhere dry bulk materials are stored and can used in a wide variety of applications, such as the following applications for example: feed, silica sand, rocks, pellets, wood, calcium dust, rubber, metals, regrind materials, coal, peanuts, malt, clays, resin, limestone, grain, foundry materials, sand pre-mix, rawhide, sawdust, and many other applications.
Monitor Technologies, LLC, the assignee of the instant application, manufactures and sells rotary paddle bin monitors, as can be seen for example at www.monitortech.com or Monitor(copyright) Bulletin 213 available from Monitor Technologies, LLC. As generally disclosed in those document, rotary paddle bin monitors are typically installed through the wall of a vessel, so that the paddle protrudes inside the vessel. A small electric motor drives a paddle which rotates freely in the absence of material. When the paddle is impeded by material, the motor rotates within the housing which triggers two switches. The first switch is a dry electrical contact closure that is available to control a process function or alarm circuit. The second switch cuts the power to the motor, preventing a locked rotor condition, thus extending motor life. This also activates the signaling device which is wired through that same motor switch. When the material level drops, the loaded stretched tension spring returns the motor to its original running position and the unit is reactivated.
While rotary paddle bin monitors such as those sold by Monitor Technologies, LLC have met with substantial commercial success, there is always a desire to improve reliability in the field or otherwise improve upon the existing technology. One area in long need of improvement has been obtaining accurate feedback about the operation of the monitor. Mechanical feedback devices such as cam lobs and contact switches are prone to wear and can influence the primary torque threshold by providing resistance that can change over time. Optical sensors have been attempted but are subject to the accumulation of dust on the lenses and related equipment. Dust can be especially problematic in dry bulk powders such as at grain elevators. Sealing the monitor housing is only effective up to a point and has not effectively eliminated the dust sufficiently for optical devices.
The present invention is directed toward the use of hall effect detectors or other magnetic sensors on rotary paddle bin monitors to provide reliable feedback about operating conditions of the monitor. The monitor may be subjected to a high dust environment in which the hall effect detectors have been found to reliably work. The hall effect detector can be used to provide feedback to indicate the relative angular position of the motor relative to the housing, and/or also the position, speed and/or direction of the rotating shaft.
The disclosed embodiment of the present invention is a bin monitor adapted to sense a level of dry bulk material in a bin or structure. The monitor comprises a housing, a shaft journalled by bearings for rotation about an axis, a paddle mounted to the shaft on the outside of the housing for engaging dry bulk material, and a rotary motor rotatable inside the housing for rotation relative to the housing. In normal operation, the rotary motor drives the shaft and thus rotates the paddle. A spring mechanism keeps the motor in a first angular position inside the housing when the paddle is rotating freely without engaging dry bulk material. However, when the paddle engages a sufficient amount of the material to create a torque that overcomes the action of the spring mechanism, the rotary motor rotates from the first angular position to a second angular position. The feedback mechanism includes a first magnetic detector mounted inside the housing and a first magnet marker fixed to the rotary motor in sensory communication with the first magnetic detector. The first magnetic detector provides an indication when the rotary motor has rotated due to the sufficient presence of bulk material. The feedback mechanism also includes second magnetic detector mounted inside the housing and a second magnet marker fixed to the shaft in sensory communication with the second magnetic detector. The second magnetic detector provides an indication that the shaft is rotating at a proper speed (and can indicate the direction of the rotation as well).
Other objectives and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.